The present invention relates to a boring bar tool used to process a bore in cutting processing work.
Boring bar tools of the kind referred to above are conventionally known; such tools are shown, for example, in FIGS. 46 through 48, FIGS. 49 through 51 and FIGS. 52 54 of the attached drawings. Each of the known boring bar tools has a tool body 11 which generally comprises a nose 2, a neck 3 in the form of a circular cylinder formed at a proximal end of the nose 2, and a shank 4, generally in the form of a circular cylinder formed at a proximal end of the neck 3. The forward end of the nose 2 has one side on which a throw-away tip (hereinafter referred simply to as "tip") 1 is mounted such that the tip 1 projects from an outer peripheral surface of the neck 2. Further, an upper rake angle a.sub.1 is given to the tip 1 under these mounting conditions, as shown in FIGS. 48, 51 and 54.
The tip 1 is generally in the form of a rhombus in plan, and is mounted to the nose 2 such that either one of a pair of cutting edges 5 and 5 formed respectively at a pair of opposed corners of the tip 1 slightly projects from the forward end of the nose 2 and the outer peripheral surface thereof.
The neck 3 has a diameter d.sub.1 which is smaller than the diameter d.sub.2 of the shank 4. That is, the diameter d.sub.1 of the neck 3 is set to a value equal to that of the nose 2 as shown in FIG. 46, or to a value smaller than that of the nose 2 as shown in FIGS. 49 and 52. More specifically, the diameter d.sub.1 of the neck 3 is set to a value equal to or less than 1.4S.sub.1 with respect to a distance S.sub.1 from an axis O.sub.1 of the shank 4 to the outermost cutting edge 5 of the tip 1 in a front elevational view of the nose 2 from the axial direction of the shank 4.
The nose 2 is formed with a chip pocket 7 for discharging, without hindrance or stagnation, chips generated by the cutting edge 5 of the tip 1. The chip pocket 7 opens to the forward end of the tool body 11 and to the outer peripheral surface thereof. The chip pocket 7 has a face 8 which is substantially flush with the face 6 of the tip 1 and an inclined surface 9 which is gradually inclined toward the outer peripheral surface of the upper portion of the nose 2 as it approaches the proximal end of the nose 2 from the rearward end of the face 8.
The boring bar tool constructed in the above manner is used as follows, to process a bore in a work, that is, to enlarge the diameter of a bore which has been formed beforehand in the work. Specifically, the shank 4 is mounted to a tool gripping section of a machining tool, for example, to the tailstock of a lathe, by means of a holder (not shown). The work is mounted to a work gripping section of the machining tool, for example, to a chuck of the lathe, so that the bore in the work has its axis oriented in a parallel relationship to the axis O.sub.1 of the shank 4. Relative movement in the axial direction of the shank 4 is given to the tool gripping section of the machining tool and the work gripping section thereof, while the work is rotated about the axis of the bore in the work, to insert the nose 2 and the neck 3 of the tool body 11 into the bore in the work. By doing so, the wall surface of the bore in the work is cut by the cutting edge 5 of the tip 1 to enlarge the bore to a predetermined dimension.
At this time, chips generated by the cutting edge 5 of the tip 1 are discharged to the face 8 of the tip pocket 7. The chips are guided toward the outer periphery of the neck 2 along the inclined surface 9 and, further, are discharged toward the proximal end of the tool body 11 through a gap between the outer peripheral surface of the neck 2 and the wall surface of the bore in the work.
In bore processing using the conventional boring bar tool described above, the bore in the work is cut under so-called cantilever conditions so that the nose 2 and the neck 3 of the tool body 11 project from the tool gripping section of the machining tool. Accordingly, the following problem arises. That is, during cutting, extreme shivering or shaking vibration tends to occur at the section of the tool body 11 extending between the nose 2 and the neck 3. Thus, the surface roughness of the cut surface deteriorates, the cutting edge 5 of the tip 1 is broken, and so on.
In order to solve the above problem, the following trial or attempt has been made. That is, the neck 3 and the shank 4 are united by cemented carbide and are brazed to the nose 2, or the diameter d.sub.2 of the shank 4 is made larger than the diameter d.sub.1 of the neck 3 as far as possible, thereby improving the tool rigidity and the attaching rigidity of the shank 4 and restricting the amplitude of the shivering or shaking vibration. However, such a trial or attempt has had the following problem. That is, if the rigidity exceeds a certain predetermined limit, the shivering or shaking vibration cannot be further reduced even if the rigidity is improved, so that there is a fixed limit to the decrease in the shivering or shaking vibration. Further, there is also a disadvantage in that copious use of the cemented carbide considerably increases the cost of the raw material of the boring bar tool.
Furthermore, in the conventional boring bar tool described above, the forward end of the nose 2 is cut out over the entire radial length thereof to form the face 8 of the chip pocket 7. Accordingly, the nose 2 is considerably lower in rigidity than the neck 3 and the shank 4. Thus the following disadvantage arises. That is, the nose 2 is easily deformed by the cutting resistance so that the height of the cutting edge 5 varies. As a result of the variation in the height of the cutting edge 5, the diameter or the like of the bore to be processed varies, so that the processing accuracy deteriorates.
Moreover, as shown in FIGS. 52 and 54, the tip pocket 7 is formed axially over a predetermined distance S.sub.2 from the forward end of the tool body 11 and radially over the entire length of the nose 2. Accordingly, there is a problem in that the forward end of the neck 2, which holds the tip 1, is low in rigidity. Further, the face 8 of the tip pocket 7 is formed so as to be flush with the face 6 of the tip 1. If the upper rake angle .alpha..sub.1 of the tip 1 increases like the side rake angle thereof, the aforesaid problem of reduction of the rigidity becomes remarkable.
If the forward end of the nose 2 is reduced in rigidity, a shivering or shaking vibration is induced during cutting, so that a bad influence is exerted upon the processing accuracy and smoothness of the finished surface of the work.